Caitlin C Conn | Search USGS

USGS2020

Thinking like a consumer: Linking aquatic basal metabolism and consumer dynamics

The increasing availability of high‐frequency freshwater ecosystem metabolism data provides an opportunity to identify links between metabolic regimes, as gross primary production and ecosystem respiration patterns, and consumer energetics with the potential to improve our current understanding of consumer dynamics (e.g., population dynamics, community structure, trophic interactions). We describe a conceptual framework linking metabolic regimes of flowing waters with consumer community dynamics. We use this framework to identify three emerging research needs: (1) quantifying the linkage of metabolism and consumer production data via food web theory and carbon use efficiencies, (2) evaluating the roles of metabolic dynamics and other environmental regimes (e.g., hydrology, light) in consumer dynamics, and (3) determining the degree to which metabolic regimes influence the evolution of consumer traits and phenology. Addressing these needs will improve the understanding of consumer biomass and production patterns as metabolic regimes can be viewed as an emergent property of food webs.

Limnology and Oceanography Letters↗

USGS2019

Water velocity regulates macro-consumer herbivory on the benthic macrophyte Podostemum ceratophyllum Michx.

1) Macrophytes influence aquatic ecosystems by increasing habitat complexity and providing trophic resources for aquatic fauna. While herbivory on freshwater macrophytes is widely documented in lakes, low-velocity riverine habitats, the influence of herbivory on macrophytes in higher-velocity habitats has rarely been examined. 2) We investigated the hypothesis that high water velocity can reduce consumption rates of the submerged macrophyte, Podostemum ceratophyllum, an angiosperm which grows attached to stable substrates in high water-velocity riverine habitats throughout eastern North America. 3) We estimated grazing-pressure by conducting short-term (up to 77-d) transplant and consumer-exclosure experiments, and quantified changes in Podostemum stem length when the plant was eposed to low (<0.5 m s-1) and higher velocities in two Piedmont rivers in Georgia (USA). Podostemum transplanted into low-velocity habitats rapidly lost stem length unless macro-consumers were excluded from accessing the plant. In contrast, Podostemum tranplanted into high-velocity habitats showed little change or gained stem length. 4) We estimated that 85% (67 – 98%; 95% credible interval) of the daily stem growth (0.026 cm cm-1 day-1) in Podostemum was consumed during a 77-d paired consumer-access versus exclosure experiment conducted in mean water velocities of 0.35-0.5 m s-1. We also found a positive relation (R2 = 0.58) between Podostemum biomass and water velocity (ranging between ~0.1 -1.4 m s-1) in benthic samples collected over a two-month period. 5) We conclude that high water velocity reduces herbivory on Podostemum, and that water velocity can thus control the acural of benthic plant biomass and the movement of plant-derived materials through benthic food webs. Our research has implications for estimating resource storage and flux in lotic food webs and illuminates a mechanism by which flow regulation and management may affect basal resources in rivers.

Georgia↗